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Semisolid preparations: Ointments, creams, pastes, gels - Coggle Diagram

- - - - Two-phase (magma): contains floccules of small distinct particles instead of large molectules.
      - Single-phase: consists of large molecules (macromolecules) uniformly distributed throughout
        a liquid with no apparent boundaries between the dispersed macromolecules and the liquid.
    - - Covalently bonded structures
        
        Direction & position of polymer chain growth during reactions = random, therefore completely disordered structures
        
        Irreversible systems
        
        Matrices are often highly rigid (i.e. hydrogels)
      - Physically Bonded Structures
        
        Predominantly disordered but containing an ordered locus
        
        Reversible systems
        
        Transition between the sol and gel phases induced by temperature and ion additives
        
        Usually formed with natural organic polymers or semisynthetic cellulose derivatives.
      - Well-Ordered Lamellar/Gel Structures
        
        rigid gels or lyogels are formed under suitable conditions
        
        Smectite clays undergo interlayer swelling spontaneously, when in contact with water, then followed by osmotic swelling to produce a gel.
        
        2 Models of plate-like clay particles (ordered, extended network)
        
        “House of cards” model: weak positively charged
        particle edges and negatively charged particle faces
        
        Flat ribbons: edge-to-edge associations of particles into flat ribbons
    - - Transitional properties
        
        Gel-sol transition (gel point)
        
        Dependent on polymer
        concentration or temperature
        
        Critical Gelling Concentration (CGC) = concentration below which no macroscopic gel is formed under prevailing experimental conditions, instead a sol is formed by polymer and solvent
        
        Physical Aging
        
        Reflects changes in gel microstructure of gels that have not attained equilibrium. Noncovalent crosslinks are breaking and reforming
        
        If polymer gels are in non-equilibrium state, instabilities can occur. 2 types of instabilities (retrogradation and syneresis).
        
        Retrogradation: spontaneous reversion of a polymer solution to a gel on standing
        
        Syneresis: process whereby liquid is liberated spontaneously from the gel matrix
      - Rheological Properties
        
        Viscoelastic substances
        
        Gels are semisolids that have both solid and liquid characteristics under stress. Under stress, ideal liquids flow and perfectly elastic solids deform
        
        Plastic flow: gel does not flow at low stresses, but only above a finite stress. Gels may exhibit thixotropy (time-dependent flow) in addition to plastic flow.
        
        Yield point (measure of gel strength) = stress at which flow begins
        
        Thixotropy occurs because the gel requires time to rebuild its original structure that breaks down during continuous shear measurements
        
        Rigidity/ shear modulus
        
        measured by the ratio of shear
        stress to strain
        
        measure of a gel's ability to resist deformation
        
        Rupture strength
        
        The stress at which a strong gel ruptures/fails rather than undergoing further strain
    - - Proteins
        
        Collagen: can form rigid gels
        
        Gelatin (denatured collaged)
      - Polysaccharides
        
        Alginates (sodium alginate, calcium alginate), carrageenan, hyaluronic acid, pectin, starch, misc carbohydrates.
      - Semisynthetic Polymers (cellulose derivatives)
        
        Methylcellulose, carboxymethylcellulose, sodium carboxymethylcellulose, hydroxypropyl methylcellulose
      - Synthetic Polymers
        
        Carbomer, poloxamer, polyacrylamide, polyvinyl alcohol
      - Inorganic substances
        
        AlOH, smectite clays
  - - - Hydrocarbon Bases (water-free bases)
        
        Examples: petrolatum, white petrolatum, yellow ointment (beeswax), mineral oil (liq paraffin)
        
        Most occlusive base, used for emollient and lubricant effects, can act as occlusive dressings, increasing skin hydration. Retains on skin for prolonged periods (difficult to wash off), prevents moisture from escaping from the skin to air (reduces rate of surface water lost).
      - Absorption Bases (w/o emulsion)
        
        Useful as emollients, but not as occlusive as hydrocarbon bases. Can also be used to incorporate aqueous solutions of drugs into hydrocarbon bases.
        
        Add lanolin, lanolin isolates, cholesterol, lanosterol, or acetylated sterols (i.e. w/o
        emulsifiers) to hydrocarbon base to make it hydrophilic
        
        Examples: lanolin, organosilicone polymers, cetyl dimethicone
        copolymer, polyethylene glycol-20-com glycerides
        
        Phase-inversion can occur when semisolid emulsion is applied to the skin.
        
        2 classes
        
        permits incorporation of aqueous solutions to form w/o emulsions
        
        w/o emulsions that permit the incorporation of small, additional quantities of aqueous solutions
      - Water-Removable Bases (o/w emulsions)
        
        Examples: vanishing cream
        
        Can absorb serous discharges in dermatological conditions.
        
        Components
        
        aqueous phase
        
        Humectants can minimize water loss in the finished product and to add to the overall physical product acceptability. E.g. glycerin, PPG, PEG
        
        Emulsifiers
        
        Anionic: acid-stable and permit adjustment of the pH to the desirable range of 4.5-6.5. E.g. sodium lauryl sulfate, phosphate esters
        
        Non-ionic: will not ionize in solutions and have excellent pH and electrolyte compatibility. Low chance of irritation. Can include a mixture of both a lipophilic and a hydrophilic member to produce hydrophilic lipophilic (HLB) balance. E.g. Sorbitan fatty acid esters, glyceryl fatty acid esters
        
        Cationic: highly surface-active, irritating to the skin, eyes and have a range of incompatibilities. DO NOT USE WITH ANIONIC MATERIALS. E.g. Cetrimide, quaternary ammonium compounds
        
        Contains emulsifiers, humectants, preservative materials and other water-soluble components/excipients.
        
        oil phase (aka internal phase)
        
        made up of petrolatum and/or liquid petrolatum to improve water-holding ability
      - Water-Soluble Bases (greaseless)
        
        Contain only water-soluble components. Difficult to incorporate aqueous solutions because they soften with the addition of water. Better used for non-aqueous or solid substances such as suppositories or pessaries.
        
        Example: polyethylene glycol (PEG)
- - - - Preparation of small qty of ointments using mortar & pestle or ointment slab & spatula using geometric dilution. Use the process of levigation or levigating agents to reduce the particle size to a minimum, avoiding roughness/grittiness of the final product.
    - - Mechanical mixers (Stainless steel kettle mixers) used for hydrocarbon and water-soluble base ointments. They can heat, cool, melt and mix oils and waxes.
      - Planetary mixers are used for mixing and sifting finely divided powders into the ointment base in a rotating mixer. The ointment preparation, once uniformed consistency is achieved, can be processes through a roller mill to disperse and reduce the size of aggregates by forcing the coarsely formed ointments through stainless steel rollers. This process ideally produces ointments that are uniform in composition and smooth in texture.
  - - - Heat to melt components
      - Allow to cool while stirring constantly until mixture is congealed.
      - Add and stir other components to the preparation while mixture is cooling
      - Add the heat-sensitive substances when temperature is sufficiently low. This is to prevent decomposition or volatilization of the components.